Electric distribution system and protective method and apparatus therefor



March 31, 1931. BURNHAM 1,798,366

ELECTRIC DISTRIBUTION SYSTEM AND PROTECTIVE METHOD AND APPARATUS THEREFOR Filed April 16, 1928 Biz/T221707.

Patented Mar. 31, 1931 UNITED STATES PATENT OFFICE GEORGE A. BURNHAM, OF SAUGUS, MASSACHUSETTS, ASSIGNOR TO CONDIT ELECTRICAL MANUFACTURING CORPORATION, OF SOUTH. BOSTON, MASSACHUSETTS, A CORPORA- TION OF MASSACHUSETTS ELECTRIC DISTRIBUTION SYSTEM AND PROTECTIVE METHOD AND APPARATUS THEREFOR Application filed April 16,

This invention relates to electric distribution systems and protective methods and apparatus therefor.

In my concurrently filed application Serial No. 270,211, I have disclosed a protective system wherein the circuit interrupter of the distribution system is opened and closed repeatedly when there is a light overload on fimprove upon the protective methods and system of said application by controlling the repeated openings and closings of the circuit interrupter in a manner and by apparatus which depends upon the strength of the overload. Thus, if the overload is moderate, the interrupter may be caused to open and close, say, eight or ten times, before it is finally held open. If, however, the overload is greater the interrupter will be held open and be prevented from reclosing after it has operated, say, three or four times. If the overload is yet greater, as due to a short circuit, the interrupter will be opened and will not reclose. If the overload which at first is light, becomes heavy, the interrupter is adapted to be maintained open and be prevented from further reclosings.

It is also an object of this invention to operate the protective system in a manner that will provide the above results and is also an object of this invention to provide apparatus by which the above results can be carried out.

A further object is generally to improve upon the protective systems and apparatus for electric distribution systems.

The figure is a diagrammatic representation of a single conductor of an electric distribution system having associated therewith 1928. Serial No. 270,212.

a protective system and apparatus embodying the present invention.

As here shown, the electric distribution system with which the present invention is associated comprises two sections and 12 which are connected to the terminals 14 of an electric switch or circuit interrupter having the movable bridging member 16, closing mechanism including the closing coil 18, and opening mechanism including the tripping or opening coil 20. The circuit interrupter is provided with an auxiliary switch having a fixed contact 22 and a movable contact 24 and connected with the operating mechanism of the interrupter by suitable means as the lost-motion connection 26. The auxiliary switch is so arranged that it closes its contacts when the interrupter is about in open position and opens its contacts when the interrupter is about in closed position.

The interrupter can be opened and closed manually by a circuit controller having the movable contact member 28, the fixed contact member 80, cooperating with the movable contact member to energize the opening coil and open the interrupter, and the fixed contact member 32 cooperating with the movable contact member to energize the closing coil 18 and close the interrupter. Power for energizing the opening and closing coils is derived from the station power buses 34. The auxiliary switch of the circuit interrupter is included in series with the closing coil 18 by means of the conductors 36 and 38. The conductor 36 is connected with one of the station buses and the conductor 40 that is connected with one of the terminals of the closing coil is adapted to be connected with the other of the station buses through the contact members 28 and 32 of the manually operated circuit controller and the conductor 42. One terminal of the opening coil is connected with one of the station buses through conductor 44 and the other terminal of the opening coil is connected to the other of the station buses through the conductor 46, the contact members 28 and 30 of the circuit controller, and the conductor 42. Thus when the circuit controller is moved to the left, the opening coil is energized and when the circuit controller is moved to the right, the closing coil is energized.

In accordance with this invention, means are provided to effect the repeated opening and closing of the interrupter on light overloads, thus to attempt to remove what may be a temporary fault on the distribution system, as the section 12, to maintain the int-errupter open when the fault degenerates first into one of a heavy overload of permanent nature, and to prevent the reclosing of the switch when it first opens if the overload initially is heavy or the fault is of a permanent nature. To this end, a. relay 48 is energized through conductors 50 from a current transformer 52 deriving its energy from the current in the section 12 of the distribution system. The relay is set to operate at a light overload and to bridge its contact members 54 which are in series wit-h the conductors 46 and 42 of the opening coil circuit, thus to open the interrupter. The current transformer also energizes the coil 56 of a lock-out relay which is set to operate at a heavy overload in the distribution system, as an overload approximating a short circuit.

Said lock-out relay is provided with normally-engaged stationary and movable contact members 58 and 60. The movable contact member 60 is biased for opening movement. Said movable contact member is held in circuit closed position by a latch 62 which is adapted to be raised when the coil 56 is sufficiently energized thus to effect the sepa ration of the contacts 58 and 60. The movable contact member 60 is adapted to remain in circuit open position until reset manually or in some other suitable manner. The contact member 58 is connected with the conductor 40 of the closing coil and the movable contact member 60 is connected through a conductor 64 with the conductor 42. The contact members of the relay are thus in series with the closing coil 18.

The operation is essentially as follows: If there is a light overload on the line, the relay 48 operates to energize the opening coil 20 and open the interrupter. \Vhen the interrupter is in open position, the contacts 22, of the auxiliary switch are closed and thus energize the closing coil 18 and effect the reclosingof the switch. If during any open period of the switch the fault on the circuit disappears the switch will remain closed after it next closes. If, however, the light fault still exists, the relay 48 again opens the interrupter. The interrupter will again close and it will be repeatedly opened and closed for so long as the light overload persists on the system.

If the fault that occasions the-operation of the relay 48 is of atemporary nature, as due to a flash-over arc, or to the bridging of the conductors of the system by a branch of a tree. or the like, the arc will be extinguished during one of the periods that the interrupter is open or the branch will be burned off during one of the momentary periods that the interrupter is closed. Thus after a few opening and closing operations of the interrupter the fault will d sappear and the interrupter when next closed and with a normal load on the line will remain closed until trouble again develops.

If, however, after a few operations of the interrupter the light fault oegeneratesinto a fault of a permanent nature or one that causes a heavy overload current to transverse the system the relay 56 will be energized sufficiently to operate and its contact members 58 and 60 will be separated. The closing coil 18 of the interrupter thus can not be energized and the interrupter will stay open until the protective system is reset manually. lf the overload current immediately at the beginning is of a high value the relay 56 will operate immediately and open the closing coil circuit so that the interrupter can not be reclosed after the relay has operated to open it. Thus the interrupter is caused to stay open whenever a heavy overload traverses the distribution system.

Preferably, although not necessarily, the interrupter opens and closes so rapidly that the synchronous apparatus connected to the system does not fall out of synchronism.

As so far described, the protective system and apparatus is essentially as described in my concurrently filed application. In accordance with this invention, means are provided to govern the number of operations of the interrupter in accordance with the load on the distribution circuit and especially when the load is less than that required to operate the look-out relay 56. Said means includes a current measuring or integrating device ind cated by the numeral 66. The device includes a container 68 which holds a body 70 of heat absorbing material as a body of oil. An electric heating coil 72 is immersed in'the oil and is energized from the current transformer'52.

A. heat-controlled normally-closed circuit controller having the stationary contact mem ber 74 and the movable contact member 7 6 is associated with the device 66. The movable contact member 76 is here shown as supported by a thermally-expansible member 7 8 which may be in the form of a bi-metallic strip composed of two metals of dissimilar coefficients of thermal expansion attached to gether back to back. Said .expansible member is immersed in the body of oil and is adapted to receive heat therefrom. When the temperature of the oil is sufficiently high, said member is adapted to expand and separate the contacts 74, 76. Y

Said thermally operated circuit controller is arranged to effect tne opening of the circuit of the closin coil T To this end,

the lock-out relay 56 is provided with an intermediate tap, and the thermal circuit c011- troller is connected with this tap and also with one of the end terminals of the coil and thus normally short-circuits the lower portion of the coil. When the expansible member 78 expands sufliciently it will separate its contact members 74., 76 and permit current to flow in the lower turns of the coil. The lock-out relay 56 will thus be effective at a relatively low current value which will be considerably less than the value at which it is intended to operate by current traversing the upper or normal portion of the coil thereof. Thus, when the thermally operated circuit controller opens its circuit, the lock-out relay will effect the separation of its contacts and the opening of the circuit of the closing coil 18.

The heating effect of the heating coil 72 is arranged to be without operative effect on the thermally operated circuit controller when a normal load traverses the distribution circuit. When, however, a light overload traverses the circuit, the interrupter will be opened and closed repeatedly and, also, eX- cess heat will be put into the oil by the heating coil 72. The amount of heat absorbed by the oil will be proportional to the strength of the overload on the line. When the temperature of the oil becomes sufliciently high, the thermally operated circuit controller will operate to actuate the lock-out relay and thus prevent the reclosing of the interrupter after a certain number of operations thereof. If the overload on the distribution circuit is moderate, the interrupter may be operated a relatively large number of times before the thermally operated circuit controller causes the opening of the closing coil circuit. If, however, the overload is of greater value the circuit interrupter will be closed a lesser number of times prior to its being maintained in open condition. The device 66 thus provides means governed by the strength of the overload on the line to govern the number of reclosing operations of the circuit interrupter. When the overload is heavy the lockout relay will be energized directly by the current transformer and immediately lockout the interrupter.

I claim:

1. The method of protecting a distribu tion system against the effects of a fault thereon which consists repeatedly in opening and closing the circuit of the system when a fault obtains on the system and in varying the number of reclosing operations in proportion to the strength of the overload current of the system.

2. The method of protecting an electric circuit against overloads which consists in opening and closing the circuit repeatedly upon overload and varying the number of reclosing operations in accordance with the strength of the overload.

3. The method of protecting an electric circuit against overloads which consists in repeatedly opening and closing the circuit when the overload is of moderate value, opening and preventing any reclosing of the circuit when the overload is of high value, and governing the number of openings and closings of the circuit on moderate overload in proportion to the strength of such overload.

4-. An electric distribution circuit having the combination of a circuit interrupter, means to open the circuit interrupter repeatedly upon overload, means to close the interrupter when it is open, and means governed by the overload to render said closing means ineffective after a number of closing operations which is a function of the strength of the overload.

5. An electric distribution system having the combination of a circuit interrupter, means to open and close the interrupter repeatedly upon overload, and means to maintain the interrupter open after a number of opening operations under amoderate overload on the system and also after a lesser number of opening operations under a heavier overload.

6. The combination of a circuit interrupter, opening and closing means for it arranged to open and close the interrupter repeatedly upon overload, means to maintain the interrupter open after a number of opening operations, and means governed by the strength of the overload in the circuit of the interrupter to govern the number of operations of the interrupter before it is maintained. open.

7. The method of protecting an electric circuit against overloads, which consists in opening and closing the circuit repeatedly upon overload and finally maintaining the circuit open and varying the number of closing operations prior to its being maintained open in proportion to the strength of the overload.

8. The method of protecting an electric circuit against overloads which consists in opening and closing the circuit repeatedly upon overload and finally maintaining it open, and decreasing the number of closing operations before it is maintained open as the strength of the overload is increased.

9. The method of protecting an electric circuit against overloads which consists in opening and closing the circuit repeatedly upon overloads and finally maintaining the circuit open, and decreasing the number of closing operations before it is maintained open as the strength of the overload is increased up to a certain strength of overload, and maintaining the interrupter open against any reclosure thereof for overloads above such strength.

10. The combination of an electric circuit, a circuit interrupter therein, and means to open and close the interrupter repeatedly upon overload and including means thereafter to maintain the interrupter open, said last-named means also including means to decrease the number of closing operations of the interrupter prior to its being maintained opened as the strength of the overload increases.

11. The combination of an electric circuit, a circuit interrupter therein, and means to open and close the interrupter repeatedly upon overload and including means thereafter to maintain the interrupter open, said last-unmet means also including means to decrease the number of closing operations of the interrupter prior to its being maintained open as the strength of the overload increases up to a certain strength of overload, and to maintain the interrupter open after the first opening thereof for overloads beyond such strength of overload.

12. A circuit interrupter having opening and closing means for it including means responsive to an overload in the circuit of the interrupter for opening and closing it repeatedly and means responsive to the strength of the overload to prevent the operation or the closing means and to maintain the interrupter open when the overload is above a certain value, and other means to prevent the operation of said responsive means when the overload is below such value.

13. A circuit interrupter having means to open and close the interrupter repeatedly upon overload, normally-inoperative means todisable the closing means and maintain the interrupter open, and a current integrating device responsive to an overload in the circuit of the interrupter controlling the operation of said disabling means to govern the number of operations of the interrupter prior to its being maintained open in accordance with the strength of the overload.

14. A circuit interrupter having means to open and close the interrupter repeatedly upon overload, normally inoperative means to disable the closing means and maintain the interrupter open, and a heat storage device in control or" said disabling means and responsive to an overload on the circuit of the interrupter ultimately to effect the disabling of the closing means and maintain the interrupter open in accordance with the strength of the overload.

15. A circuit interrupter having means to open and close the interrupter repeatedly upon overload, overload responsive means to effect repeated opening and closing operations of the interrupter, and a heat storage device including means responsive to the strength of the overload in the circuit of the interrupter ultimately to disable the closing means and maintain the interrupter open.

16. A circuit interrupter having means to open and close the interrupter repeatedly upon overload 'inthe circuit of the interrupter, an overload responsive relay associated with the opening means to effect the opening of the interrupter upon overload, means including a thermally operated circuit controller associated with the closing means to disable said closing means and maintain the interrupter open, and a heat storage member associated with and controlling theoperation of said thermally operated circuit controller adapted to become heated upon overload and to store up heat in response to the strength of the overload and finally operate said thermally operated circuit controller.

' 17 An electrical distribution system having the combination of a circuit interrupter, opening and closing means to open and close the interrupter repeatedly upon overload, means operative at some time after the occurrence of the overload to disable the closing means and leave the interrupter open, and means governed by the strength of the overload to vary the time at which said disabling means effectively operates.

18. In combination with a circuit interrupter, normally-operative overload-governed means to open the interrupter upon overload and thereupon to close it and means to maintain the interrupter open after a number of closin 'operations that varies with the strength of the overload.

In testimony whereof, I have signed my name to this specification.

GEORGE A. BURNHAM. 

